Stabilizing Fabry-Perot optical frequency comb with differential phase detection and bias compensation.

We present a stable optical frequency comb (OFC) that utilizes a Fabry-Perot phase modulator. The environmental-induced state variation of the OFC is accurately detected by measuring the relative phase changes of beat signals from its upper and lower sidebands. We then compensate for this variation by controlling OFC bias voltage through a homodyne phase-locked loop. The differential phase detection eliminates the common-mode detection noise, enabling long-term stability of the OFC without requiring any additional reference signal. The relative phase change is only 0.056° over 3800 s. Even under a drastic temperature change, the OFC remains stable, validating the effectiveness of the proposed stabilization method.